The following description includes information that may be useful in understanding the present disclosure. It is not an admission that any such information is prior art, or relevant, to the presently claimed inventions, or that any publication specifically or implicitly referenced is prior art.
Electropermeabilization of mammalian cells is a technique that has been used for delivery of therapeutic substances including small molecules, such as anticancer agents bleomycin and cisplatin, and macromolecules such as nucleic acids and proteins. Typically, delivery of such substances into cells is brought about by injecting the substance into the tissues containing the cells, which injection merely places such substance into the interstitial spaces between the cells, followed by physically contacting the tissues with a metallic electrode of one configuration or another and applying an electric potential across the electrodes. Usually, the electrode is manifest in the form of at least two opposing needle-like tissue piercing rods or tubes comprising an anode and a cathode. Other forms of tissue contacting electrodes include non-penetrating electrodes such as planar pads as found in “caliper” electrode devices such as disclosed in U.S. Pat. No. 5,439,440 and meander electrodes such as disclosed in U.S. Pat. No. 6,009,345. Still other electrode types have included minimally invasive electrodes such as disclosed in U.S. Pat. No. 6,603,998.
With regard to the electrodes as mentioned above, all operate within a paradigm well understood in the electrical arts to require express and direct contact between the electrode and the tissue undergoing electropermeabilization. Further, the electrical potential placed across the positive and negative poles, often expressed as “field strength” in Volts/centimeter, has been in the vicinity of tens to hundreds of volts per centimeter, i.e., voltage potential between the positive and negative poles spaced apart in, or on, the tissue a given distance. Typically, distances between electrodes are from tenths of centimeters to full centimeters of length. In most disclosures concerning electropermeabilization, the voltages required to provide a field strength sufficient for cell poration in the tissues are anywhere from one Volt for skin tissues to upwards of five or six hundred volts for cells lying in deeper body tissues. The various levels of voltage applied are typically dependent upon the spacing of the positive and negative electrodes and the electric resistance of the tissue undergoing treatment.
There have been many recent advances in the art of electropermeabilization wherein low voltage potentials have been applied to skin tissues. In many of these cases, the low voltage applied has been tied to very lengthy time periods for applying the electrical energy. In some cases, the electrical energy has been applied in a direct current form understood in the arts as providing an electrophoresis or iontophoresis effect wherein substances are moved through the tissue slowly. In such conditions and particularly with small molecules, the electric pulses only provide for the molecules to be moved through tissue interstitial space, not inside the cells within the tissue. Even where the low voltage has been applied for short periods of time, the electrodes comprise the typical complex two pole array arrangement, i.e., for example, at least one each of independently chargeable cathode(s) and anode(s) placed in contact with the tissues. Other recent disclosures discuss the use of very high voltages, in the 10,000 plus Volt range, for very short time periods to achieve delivery of substances into cells but none the less require contact of the electrodes with the tissue.
Whether using low or high voltages, tissue contacting electrodes systems are subject to practical limitations primarily concerning safety and comfort, or lack thereof, to the mammal undergoing treatment. There is also the practicality or impracticality of manufacturing complex miniaturized arrays containing both anodes and cathodes often organized to be pulsed independently of one another in various sequences and direction of pulsing. Use of high voltages with tissue piercing and surface touching electrodes can be dangerous for the potential of severe electric shock if conditions include high amperage over a time greater than 10 millisec. Use of low voltages over an extended period of time, though typically not dangerous, has the potential of being uncomfortable to the patient mammal or otherwise requires complex manufacturing processes. In addition, there are concerns that voltage facilitated systems or delivery methods result in low levels of efficacy.
Still other issues are of concern in delivery of substances to skin or tissue surface cells. For example, some systems disclose methods of delivering the substance through the skin surface, i.e., the stratum corneum, followed by delivery of the electric potential with the typical tissue penetrating or surface contacting electrodes. With regard to such substance delivery, instead of direct injection some systems attempt to draw the substance directly through the stratum corneum by iontophoresis and/or electrophoresis by applying various means to first ablate the stratum corneum before providing the substance and electric potential. For example, one system uses a laser beam to poke holes in the stratum corneum (U.S. Pat. No. 6,527,716). Another uses a high intensity tissue ablating spark not unlike a cauterizing surgical instrument (U.S. Pat. No. 6,611,706). In each of such systems, the methodology relies on physically disrupting the stratum corneum in order to deliver the substance and further aid in the transmission of the electrical energy from the tissue contacting electrodes into the tissue.
Thus, there is in the art a need to advance delivery of substances into cells using electropermeabilization in a manner that avoids electrical hazards, discomfort to the treated patient, damage to the tissues, and complex manufacturing.